The United States has imposed visa restrictions on individuals and institutions it says are "threatening the sovereignty and territorial integrity of Ukraine."

A senior U.S. official said the visa bans apply to both Russian and Ukrainian officials.

In a statement on March 6, the White House said that President Barack Obama had also signed an executive order that authorizes sanctions against "individuals and entities responsible for activities undermining democratic processes or institutions in Ukraine."

Senior U.S. officials said the executive order was "a powerful tool" that gives the Obama administration flexibility to calibrate its response to Russia's occupation of Crimea and respond to possible escalation.

The new action on visas comes in addition to U.S. sanctions on individuals involved in human rights abuses related to political oppression in Ukraine.

The White House said the United States was prepared to consider additional steps depending on how the situation develops in Ukraine.

The visa restrictions were announced as U.S. Secretary of State John Kerry headed into a meeting with Russian Foreign Minister Sergei Lavrov in Rome.

Lavrov said afterward Kerry had assured him there are no blacklists of Russian officials as yet. However, Lavrov said any intentions to impose sanctions were already a threat.

The White House announcement comes as EU leaders are discussing a response to the occupation of Ukraine's Crimea region by Russian forces.

In other news, the Pentagon said a U.S. Navy destroyer was heading to the Black Sea for what it says were previously planned exercises.

Officials say the "U.S.S. Truxtun," a guided-missile destroyer, is due to take part in a military exercise involving Romanian and Bulgarian naval vessels.

A statement from the U.S. Navy said, "While in the Black Sea, the ship will conduct a port visit and routine, previously planned exercises with allies and partners in the region."

U.S. officials denied any connection to the crisis in Ukraine, where Russian forces are occupying the Crimean Peninsula, the home of Russia's Black Sea Fleet.